Radiator fin-tube construction and method

ABSTRACT

Fin-tube radiator core construction and method in which the fins are formed by folding a strip of sheet metal back and forth on itself and perforations are formed at the fold lines of the fins adjacent the tubes for receiving projections of adhesive from the coating thereof on the surface of the tube to create a strong bond between the fins and the tubes.

[ 51 Sept. 26, 1972 United States Patent Drosnin [54] RADIATOR FIN-TUBE 2 5 m mm Tm m mm .m Wm A w M m TO N m 7 mm NM m m 6 0 7 7 CONSTRUCTION AND METHOD [72] Inventor:

Sidney S. Drosnin, 2087-l0th Ave., San Franclsco Cahf' 941 16 Primary Examiner-Frederick L. Matteson April 20, 1970 Assistant Examiner-Theophil W. Streule [22] Filed:

Attorney-Boyken, Mohler, Foster & Schwab 211 Appl. No.2 29,862

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formed at the fold lines of the fins adjacent the tubes [56] References Cited for receiving projections of adhesive from the coating 'UNITED STATES PATENTS thereof on the surface of the tube to create a strong bond between the fins and the tubes. 1

Wall et al. ............165/184 Gier, Jr......................165/15l 6 Claims, 9 Drawing Figures 68 66 99 11 ll 0 ll.

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ooooooocaoooooo 4 OOO O01 66 6 6 00000 OOOOO! 6 Q 6 6 00000 a m F irrae/vlfs' RADIATOR FIN-TUBE CONSTRUCTION AND METHOD BACKGROUND OF THE INVENTION Two types of radiator fin-tube constructions are generally in use for automotive radiator and heater cores and the like, in which a plurality of elongated tubes are connected at their opposite ends to headers for circulating fluid to be cooled, and a plurality of l spaced, generally parallel, sheet metal fins extend transversely of the tubes for exposing a greater heat radiating surface to the heat-dissipating media, com= monly air. The continuous-fin type, in which the fins are elongated, parallel, spaced strips of sheet metal provided with openings through which the tubes are transversely inserted, has the advantage that the adhesive bond between the tubes and the fins (commonly metal soldered) is less likely to be broken during expansion and contraction of the tubes due to temperature and pressure changes encountered in use, and therefore the heat transfer contact between them is more likely to be maintained. This type of core is much more difficult and expensive to construct, however, because the openings in the fins must be in accurate register and closely receive the tubes to achieve a satisfactory engagement and bonding between them.

In another type of radiator core construction currently in use, ribbon-shaped stacks of fins are formed by folding an elongated strip of sheet metal back and forth on itself and securing tubes to the opposite folded edge portions of the fin stack. Similarly, bonding has usually been accomplished by applying heat and pressure to an assembled core of tubes and fin stacks to cause a metal solder coating on the tubes to adhere to the edge portions of the fins.

Although this type of core is much more readily and inexpensively fabricated, and has a substantially greater cooling capacity, the bond between fins and tubes is more easily broken by expansion and contraction of the tubes due to pressure and temperature variations; thereby interrupting the contact between fins and tubes and substantially decreasing the efficiency and structural integrity of the core.

SUMMARY OF THE INVENTION This invention relates to the provision, in the latter type of folded-fin radiator construction, of a plurality of small perforations in the folded edge portions of the fins adjacent the tubes which receive portions of the solder or other adhesive coating from the tube during the bonding process. A number of rivet-like projections of adhesive are received in the fin perforations thereby strengthening the bond many-fold over the prior construction method and maintaining the tube-fin contact over extended periods of use and excessively rigorous temperature and pressure variations.

This invention includes not only a radiator core structure fabricated as above described, but also the provision of a method for forming the fins and for constructing a radiator core from such fins and conventional tubes. The perforations may be formed in the strip of sheet metal prior to or during the folding of said strip into a stack of generally parallel, spaced fins.

It has also been found that the formation of small projecting ridges around the perforations in the folded edge portions of the fins contributes significantly to the bond between the fins and the tubes, particularly when such ridges project outwardly of the folded portions at the edges of the fins toward the tubes.

It is therefore an object of this invention to provide, in a fin-tube structure for a radiator core of the type wherein the fins are formed from a folded strip of sheet metal, an adhesive bond between the folded edgeportions of the fins and the tubes of sufficient strength to 0 withstand repeated and extreme pressure and temperature variations. 1

Another object of this invention is the provision of a method of forming a radiator core of the folded-fin type wherein the adhesive bond between the fins and the tubes is substantially the equivalent of the corresponding bond in a radiator core of the type in which the tubes extend through openings in the fins.

It is a further object of this invention to provide a method of forming radiator fins which may be readily assembled with and attached by a long-lasting bond to tubes in a radiator core.

Other objects and advantages will appear from the following detailed description of preferred embodiments of the invention, illustrated in the accompanying drawings in which:

DESCRIPTION OF FIGURES FIG. 1 is an enlarged front elevational view of a portion of a radiator core fabricated in accordance with this invention;

FIG. 2 is a sectional view as seen from line 2-2 of FIG. 1;

FIG. 3 is a greatly enlarged sectional view as seen from line 3-3 of FIG. 1;

FIG. 4 is a semi-diagrammatic view of a form of apparatus and illustrating'a method for forming radiator fins in accordance with this invention;

FIG. 5 is a top plan view of the apparatus of FIG. 4;

FIG. 6 is a greatly enlarged sectional view of the fin perforation fonning apparatus illustrated in FIG. 4;

FIG. 7 is a sectional view as seen from line 77 of FIG. 6;

FIG. 8 is an enlarged view of a portion of the apparatus of FIG. 4, showing a modified form of apparatus and illustrating a method for forming the radiator fin construction of this invention; and,

FIG. 9 is a partial sectional view, similar to FIG. 3, showing a modified form of fin-tube bond construction.

DESCRIPTION OF PREFERRED EMBODIMENTS- RADIATOR CORE In a fin-tube radiator of the folded-fin type herein described, the core 1 (FIGS. 1-3) is formed from a plurality of hollow, elongated tubes 2 of oval cross section connected in spaced, parallel relationship at their ends to communicate with fluid-containing headers 3. A plurality of generally parallel, spaced fins 4 extend transversely between tubes 2 and the assembly is bounded by opposed sidestraps 5 secured at their ends to headers 3. Fins 4 are normally formed in stacks 8 by folding a strip of sheet metal back and forth on itself and the opposite edge or folded portions 6 are secured in heat-transfer engagement to the tubes 2 by an adhesive, such as solder coating 7 (FIG. 3) on the outside of tubes 2.

It is obvious that tubes 2 function to, circulate fluid, such as water, between headers 3. The purpose of fins 4 is to provide extensive heat-exchange surface to transfer heat from or to the fluid in tubes 2 to be radiated to or from a medium, commonly air, flowing past the tubes and fins.

Since such a radiator core is subjected during use to wide variations in temperature and pressure, it is essential to the performance of this function that a strong bond be maintained between fins 4 and tubes 2. ln automotive use, for example, the watertemperature in tubes 2 may vary from below freezing to substantially above the boiling point at atmospheric pressure. In modern pressurized automobile cooling systems the pressure varies between atmospheric and 18 psi. The cycling between these extremes expands and contracts tubes 2 and continually flexes the tube walls, the edge portions 6 of fins 4 and theadhesive bond therebetween.

In order to provide and maintain satisfactory heattransfer engagement between fins 4 andtubes 2 over an extended period under such conditions of use, this invention contemplates forming a plurality of relatively small perforations 10 along the folded edge portions 6 of fins 4. Perforations 10 are distributed in spaced relation along the opposed fold lines or edges 6 of the stacks 8 of fins 4 adjacent the flattened sides 11 of tubes 2 (FIGS. 2, 3). When the stacks of fins 4 and tubes 2 having a solder or other suitable adhesive coating 7 thereon are assembled and subject to heat, it has been found that small portions 12 of solder are received .in perforations .10. It is believed that the solder portions 12 are attracted into perforations 10 by capillary action, and upon setting or solidification of the solder, portions 12 provide rivet-like projections in perforations 10.

As seen in FIG. 3 in the preferred form of the invention, a frustoconical wall or ridge 13 surrounds each perforation 10. Therefore, the portion of solder 12 that is received therein from the coating 7 on tube 2 diverges outwardly away from the tube forming a button or head 14 atthe innersurface of folded edge portions 6 of fins 4.

Tubes 2 and fins 4 are normally made from relatively thin sheet metal, such as copper, the tube walls being of the order of 0.004 inch thick and the fins being of the order of 0.0025 to 0.003 inch thick. The solder coating 7 may be of the order of 0.001 inches thick. Relatively, the divergent outer end of a perforation 10 (FIG. 3) is preferably approximately 0.030 inch in diameter; whereas the inner convergent end of said perforation has a diameter of approximately 0.006 to 0.010 inch. The wall 13 surrounding each perforation 10 preferably projects outwardly from the outer surface of folded edge portion 6 approximately 0.006 to 0.008 inch and the center-to-center spacing of perforations 10 is preferably in the range of 0.055 to 0.058 inch.

It is believed that directing frustoconical wall 13 toward side 11 'of tube 2 and maintaining that relationshipunder pressure during the fabrication of the radiator core of this invention facilitates the formation of solder portion 12 in perforation 10. It will also be noted in FIG. 3 that other portions 15 of solder from coating 7 flow and solidify around the outside of frustoconical walls 13, thereby contributing to the strength of the bond and enhancing the heat-transfer contact between tubes 2 and fins 4. Utilizing the construction of this invention may realize substantial savings in materials, as significantly thinner strips may be employed for the formation of fins 4 than heretofore.

Comparative tests were run on radiator cores fabricated under'identical conditions and using identical materials according to:

1. Conventional construction in which the plain, folded edge portions of the fins were soldered to the tubes, and

2. The construction described herein in which the folded edge portions of the fins included perforations I0 and walls 13. Upon varying the water pressure in the radiator core tubes between zero and 25 psi every 15 seconds, after approximately 8 hours the conventional core had expanded and the bonds between tubes and fins failed to the extent that its cooling efficiency and structural integrity were effectively destroyed. After 30 hours of testing under the same conditions, the core fabricated in accordance with this invention remained intact. When the maximum pressure was increased to 45 psi the conventional core failed within 40 minutes; whereas the core made in accordance with this invention lasted 18 hours before failure.

Similar testing in which the water pressure in the tubes was cycled between zero and 32 psi every 7% seconds resulted in overall expansion of the conventional radiator core of one-eighth inch within one-half hour, which degree of expansion is beyond tolerable limits for utility. Tested under the same conditions a radiator core fabricated per (2) above had anoverall expansion of only one-sixteenth inch after 10% hours.

APPARATUS AND METHOD Except for the perforating rollers '19, 20 at the right hand end, the apparatus of FIGS. 4 and S is that conventionally used to fold an elongated strip of sheet metal 21 into a stack 8 of fins 4. That apparatus initially crimps strip '21 which is approximately as wide as the finished radiator core 2) alternately oppositely along transverse fold lines 6by a pair of meshed star wheels 22, 23. Strip 21 is thus folded into alternately opposed approximately V shapes, and star wheels 22, 23 may also be provided with cutting-edge dies for forming slits (not shown) in the strip between fold lines 6 for facilitating air circulation.

The partly folded strip 21 is then fed into a trough 24, having opposed side walls 25, a bottom wall 26 and upper guides 27 spaced upwardly from the bottom wall approximately the width of the finished fins. A paddle wheel 28 having paddles 29 with rounded ends radiating therefrom is supported for rotation in trough 24 between guides 27 and serves to form rounded fold portions at fold lines 6 and to compress the intervening fin portions 4 of strip 21 together against the frictional resistance provided to the folded stack 8 by guides 27, bottom wall 26, and a pair of rubber-surfaced drag wheels 30 supported above and below trough 24 (F IG. 4). The friction exerted by trough 24 may be varied by adjusting the height of guides 27 with adjusting screws 31 and the drag applied by wheels 30 may be varied by an adjustment mechanism 32 operatively connected thereto (1 16.5).

Wheels 22, 23, 28, and 30 are suitably journalled for rotation in bearings supported on a main frame 33 and, except for the wheels 30, are connected to main drive gearing 34 (FIG. 5) to be driven synchronously. The apparatus. thus alternatively folds strip 21 back and forth on itself to provide an endless stack 8 of fins 4 connected by folded edge portions 6. The endless stack is then cut to lengths suitable for assembly with tubes 2 into a radiator coreas heretofore described. It will be understood that other types of apparatus are conventionally available for forming such stacks of fins.

This invention contemplates adding to the conventional portions of the apparatus of FIGS. 4 and 5 perforating rollers 19, 20 which are cylindrical in configuration and provided with alternate rows of pointed pins 37 extending radially outwardly from the circumferential surfaces thereof and recesses 38 extending radially inwardly from said circumferential surfaces. The rows of such pins and recesses are distributed around the circumferential surfaces of rollers 19 and on the same spacingas between the lines 6 at which strip 21 is to be folded, and the pins of roller 19 are positioned to mesh with and project into the corresponding recesses in roller 20 and vice versa.

As shown in FIGS. 6, 7 pins 37 are spaced axially of rollers 19,- 20 corresponding to the desired spacing between perforations l0 transversely of strip 21 and are supported in an insert 39 with their points projecting outwardly of the periphery of the respective r0] lers.'Recesses 38 may be in the form of axially elongated slots or individual bores, spaced corresponding to It will be understood that pins 47 may project from and recesses 48 may be formed in either the valleys or ridges of star wheels 42, 43. In the form shown. in FIG. 8 pins 47 and recesses 50 cooperate to form ridges 63 surrounding perforations 60 projecting inwardly of the folded portions 56 defining the edges of fins 54 formed in a strip 51.

This modified form of fin construction is shown in FIG. 9 associated with a tube 52, identical to tube 2. It will be noted that a similar adhesive or solder coating 57 on tube 52 flows into and is received in perforations 60 the frustoconical walls 63 of which converge inwardly of folded edge portion 56 of fins 54 away from tube 52. Solder portion 62 similarly forms a rivet-like projection in each perforation 60 with an enlarged head 64 on the inner side of folded edge portion 56. One of the advantages of the modified construction of FIG. 9 is that a larger surface area of folded portion 56 is in contact with the fiat wall 61 of tube 52 thereby providing additional heat transfer engagement'and adhesive securing area. It has been found, however, that the overall strength of the bond between fins 54 and tubes 52 is slightly less than the corresponding bond in the preferred form of the invention disclosed in FIG. 3.

Although the invention has been described and illustrated in detail, other modifications that would occur to those skilled in the art are intended to be included within the spirit and scope of the appended claims. For

0 example, perforations 10, 60 may be in the form of one pins 37, opening outwardly of rollers 19, 20 and formed in hardened inserts 41. Thus, the point 40 of a pin 37 serves as a male die cooperating with a female die provided by a recess 38 (FIG. 6) to punch perforation 10 and form thesurrounding frustoconical wall 13 in strip 21 as the same passes between rollers 19, 20.

Said rollers are suitably journaled for rotation in bearings on main frame 33 (FIGS. 4, 5) at a location spaced from star wheels 22, 23 such that the rows of perforations l0 are formed in strip 2l directly on the lines 6 at which star wheels 22, 23 subsequently crimp or fold said strip. Pins 37 and recesses 38 alternately form walls or ridges l3 projecting downwardly and upwardly and,-to create the preferred embodiment of fin construction shown in FIG. 3, star wheels 22, 23 correspondingly fold strip 21 at such rows of perforations downwardly and upwardly, respectively. Rollers 19, 20 are connected by suitable gearing 36 (FIG. 5) to the main drive and gearing 34 of the fin forming apparatus.

As an alternative form of apparatus for forming perforations l0 and ridges 13, a modified form of star wheels 42, 43 (FIG. 8) may be employed. Said latter star wheels are similar in construction to wheels 22, 23 except they are provided with rows of pointed pins 47 and recesses 48 extending axially along their valleys and ridges 46.

In this modification the sharpened point 50 of a pin 47 projects upwardly of a valley 45 on one of star wheels 42, 43 into a recess 48 in the ridge 46 of the other star wheel to form perforation 10 and ridge 13 at the fold line 6 of an elongated strip 51 of fin material at the same time the initial fold is formed therein by the star wheels 42, 43.

or more elongated slits extending longitudinally or transversely of fold lines 6, 56. Although perforations in the form of circular openings as illustrated have the effect of more readily facilitating a flattened fold portion at lines 6, 56, short transverse slits in their place accentuates this characteristic, providing an increased bonding area with tubes 2, 52.

Iclaim:

1. In an automobile radiator core including a plurality of spaced, generally parallel elongated tubes and a plurality of strips of sheet metal individually folded back and forth on themselves to provide stacks of generally parallel spaced fins connected by arcuate, folded portions, said stacks extending transversely between said tubes and adapted to be bonded thereto at said folded portions in heat transfer engagement, the improvement comprising:

a. an elongated row of spaced perforations extending along said folded portions;

b. generally frustoconical walls formed in said folded portions surrounding said perforations; and

c. portions of an adhesive coating adhered to said tubes and received through said perforations and within said frustoconical walls and at least substantially filling said perforations and the space within said frustoconical walls for securing said stacks to said tubes.

2. The automobile radiator core according to claim 1 in which:

(I. said portions of adhesive coating fill said perforations and space within said frusto-conical walls and are provided with enlarged heads on the side of said portions opposite said tubes.

3. The automobile radiator core according to claim 2, in which:

e. said perforations are generally circular;

4. The automobile radiator core of claim 1 in yvhich:

d. other portions of said adhesive coating are received around the outside surfaces of said frustoconical walls. 5. The automobile radiator core of claim 1 in which:

d] said frustoconical walls converge outwardly toward said tubes. 6. The radiator core of claim 1, in which: d. at least one dimension of said perforations is of the order of three to ten times the thickness of said fins. 

1. In an automobile radiator core including a plurality of spaced, generally parallel elongated tubes and a plurality of strips of sheet metal individually folded back and forth on themselves to provide stacks of generally parallel spaced fins connected by arcuate, folded portions, said stacks extending transversely between said tubes and adapted to be bonded thereto at said folded portions in heat transfer engagement, the improvement comprising: a. an elongated row of spaced perforations extending along said folded portions; b. generally frustoconical walls formed in said folded portions surrounding said perforations; and c. portions of an adhesive coating adhered to said tubes and received through said perforations and within said frustoconical walls and at least substantially filling said perforations And the space within said frustoconical walls for securing said stacks to said tubes.
 2. The automobile radiator core according to claim 1 in which: d. said portions of adhesive coating fill said perforations and space within said frusto-conical walls and are provided with enlarged heads on the side of said portions opposite said tubes.
 3. The automobile radiator core according to claim 2, in which: e. said perforations are generally circular; f. the convergent end of said frustoconical walls has a diameter of approximately 0.006 to 0.010 inch and the divergent end thereof has a diameter of approximately 0.030 inch; and g. said frustoconical walls project outwardly from the surface of said folded portion approximately 0.006 to 0.008 inch.
 4. The automobile radiator core of claim 1 in which: d. other portions of said adhesive coating are received around the outside surfaces of said frustoconical walls.
 5. The automobile radiator core of claim 1 in which: d. said frustoconical walls converge outwardly toward said tubes.
 6. The radiator core of claim 1, in which: d. at least one dimension of said perforations is of the order of three to ten times the thickness of said fins. 